Reactive sputtering is performed in a magnetron sputtering system. The material sputtered from the magnetron is combined with a reactive gas at the substrate (item being coated) to form a compound at its surface. The reactive gas also reacts with the target surface, forming a compound there. These systems can operate open loop in either the metallic mode, where a small fraction of the target is covered with the compound, or the poisoned mode, where a large fraction of the target is covered with compound. In some cases, the compound has a sputtering yield much lower than the native target material. In fact, the sputtering yield for a target completely covered with reactive compound (poisoned) can be 10% or less that of the native target material. Because of this, it is desirable to run these processes in the transition mode, to achieve a higher deposition rate. The transition mode is typically inherently unstable, so feedback control is usually required to stabilize the process there. Feedback can be, for example, process voltage, reactive gas partial pressure, and optical emission from the target.
A common implementation of reactive sputtering is dual magnetron sputtering (DMS) shown in FIG. 1. A key advantage is the absence of explicit anodes, and the challenges that come with them. The two magnetrons alternate roles as cathode and anode. When a purpose built bipolar pulsed supply is used to drive the process, the power to each magnetron can be regulated individually. Fast read backs of power, voltage, and current for each magnetron can be provided to the user for use in monitoring and controlling the process.